1. Field of the Invention
The present invention relates to an optical pickup used for an optical disc apparatus and to the optical disc apparatus.
2. Description of the Related Art
In an optical disc apparatus using an optical pickup, various technologies have been proposed for tracking control of an objective lens in the optical pickup. For example, Japanese Laid-open Patent Publication Hei 8-249684 discloses a technology to extract a tracking error signal at a predetermined position of an optical pickup, when moving the optical pickup at a high speed, so as to use the tracking error signal to prevent a change in position of a tracking actuator, a light beam and a photodetector. Japanese Laid-open Patent Publication 2000-173066 discloses a technology to short-circuit both ends of a tracking coil during rough seek and until entering into initial tracking pull-in operation so as to generate an induced electromotive force to be used for controlling the vibration of an objective lens. Further, Japanese Laid-open Patent Publication Hei 8-329479 discloses a technology to provide a switch for connecting a signal from a differential amplifier circuit to optical pickup moving means for servo to fix an objective lens system at a certain position relative to the moving system by closing the switch when the optical pickup moves in a direction perpendicular to the tracks for retrieval.
However, these technologies have problems as described below. More specifically, in some cases, an optical disc with an offset or eccentric center of gravity may be mounted on an optical disc apparatus. When such an optical disc with an offset center of gravity is rotated on a turntable at a high speed, the optical disc itself vibrates strongly. The vibrations of the optical disc are transmitted to the optical pickup via the turntable, a spindle motor and a shaft for supporting the optical pickup. When the optical pickup is vibrated excessively, the objective lens for irradiating a light beam to the optical disc is also vibrated strongly and displaced in e.g. a tracking direction, giving a bad influence to the light received by a photodiode (photodetector). As a result, it becomes impossible to obtain an appropriate tracking error signal, which may cause unstable tracking servo control and failure in tracking pull-in. More specifically, if an appropriate tracking error signal cannot be obtained, even the technology of Japanese Laid-open Patent Publication Hei 8-249684 described above may cause unstable tracking pull-in. Further, the technologies of Japanese Laid-open Patent Publications 2000-173066 and Hei 8-329479 described above cannot stabilize the tracking pull-in.